A touch screen has replaced button switches as a user input device in order to provide light weight and a thin profile to household appliances and electronic devices. The touch screen is a device configured such that a user directly touches the screen without the use of other input devices and input information. Touch screens are now being used in the cellular phone market and have been widely used in most IT products.
The touch screen used in a display device includes a plurality of touch sensors and may be attached to a display panel of the display device. The touch screen may be classified into a resistive type touch screen, a capacitive type touch screen, an electromagnetic type touch screen, etc. based on its touch recognition manner. The capacitive type touch screen, which senses a position having changes in a capacitance and senses a touched portion, has been widely used.
As shown in FIGS. 1 and 2, a capacitive type touch screen includes a plurality of Tx electrode lines T1 to Tn, a plurality of Rx electrode lines R1 to Rm crossing the Tx electrode lines T1 to Tn, and a plurality of touch sensors formed at crossings of the Tx electrode lines T1 to Tn and the Rx electrode lines R1 to Rm, where m and n are a natural number. Each of the touch sensors is implemented as a mutual capacitor Cm. When a user touches the capacitive type touch screen with his or her finger, etc., an electric field between Tx and Rx electrodes of the mutual capacitor Cm is blocked. Hence, the amount of charge of the mutual capacitor Cm decreases. The touch sensors sense changes in the charge amount of the mutual capacitor Cm before and after a touch operation. For this, a charge voltage of the mutual capacitor Cm is readout to a readout integrated circuit (ROIC) through the Rx electrode lines R1 to Rm when a touch driving pulse is supplied to the Tx electrode lines T1 to Tn.
A display panel of a display device includes a plurality of data lines D1 to Dm to which a data voltage is applied. The Rx electrode lines R1 to Rm extend in the same direction as an extending direction of the data lines D1 to Dm and may partially overlap the data lines D1 to Dm. In this instance, the Rx electrode lines R1 to Rm and the data lines D1 to Dm, which partially overlap each other, are coupled to a parasitic capacitance Crx between the lines R1 to Rm and D1 to Dm.
Changes in a potential of the data lines D1 to Dm affect a potential of the Rx electrode lines R1 to Rm because of the parasitic capacitance Crx, thereby leading to a coupling noise. The coupling noise is mixed in a touch signal and thus greatly reduces a touch performance of the touch screen. As the coupling noise increases, a sensing value obtained by the touch screen may be excessively distorted. Hence, an undesired touch result may be obtained. Accordingly, a method for increasing a sampling rate (defined by the number of sampling operations per unit of time, for example, during one touch frame period) of sensing voltages readout by the touch sensors may be considered, so as to reduce the coupling noise. However, in this instance, the power consumption of the ROIC also increases.